Furling sails are known in the art. They are generally a jib that may be wrapped about a stay for storage when not in use. The wrapping of the furling sail allows the sail to be easily stored and deployed. As illustrated in FIG. 1, a furling sail 6 is typically attached at its base to furling drum 4, which may be wound and unwound using an attached rope 8 to deploy and retract sail 6 (illustrated as partially unwound). The head of the furling sail is attached to a support such as the sailboat masthead 10 using swivel 2, while the tack of the sail is attached to the rotating furling drum 4. The swivel 2 and drum are connected to one another by foil 12, which rotatably rides over a headstay. The swivel 2 generally has a top body element that is attached to the masthead, and a lower body element attached to the furling sail head and that rotates with the drum 4 as the furling sail is wound and unwound around the foil 12.
Further detail regarding furling systems and furling swivels of the prior art is available in the 1999 products catalogue of Harken Inc., Pewuakee Wis., USA; incorporated herein by reference. In particular, attention is drawn to furling systems comprising drums and swivels illustrated on pages 115-129 of the catalogue.
A number of heretofore unresolved problems exist with furling systems. The furling sail swivel and drum must anchor a sail that may be under very heavy wind loads. Additionally, the swivel and drum must withstand severe weather conditions. With these considerations in mind, furling swivels and drums are generally of relatively robust and heavy construction. The swivel and drum typically have an extended tang with an eyelet through which a stainless steel linkage piece such as a clasp or bracket connects to the sail. The relatively heavy construction of the tang and brackets used to attach the sail head and tack are disadvantageous for sailing vessels, as there is a desire to keep weight to a minimum. Further, the swivel is located at the top of the furling sail high up in the rigging of a sailing vessel. This compounds the effects of its relatively heavy weight, as weight high aloft is particularly disadvantageous because it increases heeling of the boat.
The clasps or brackets used to attach the sail head and tack may disadvantageously deform or even fail through fatigue. This results from the stresses sails are under in combination with the extreme weather conditions the clasps or brackets are exposed to.
An additional unresolved problem with furling sail swivels and drums relates to their wind drag characteristics. It is desirable for sailing vessels to have minimal wind drag, particularly aloft. The extended tang on the furling system drum and swivel result in disadvantageous wind drag characteristics.
The tang and bracket used to attach the sail to the swivel and to the drum are also disadvantageous for reasons in addition to weight and wind drag. In particular, the length of the tang increases the bending moment on the swivel and drum. Also, the tang concentrates the bending stress on a small portion of the swivel or drum. As the drum or swivel rotates, this increased and concentrated bending moment is passed on to a small portion of the bearings or other rotation facilitating means used by the drum or swivel. This disadvantageously increases frictional resistance to rotation of the drum or swivel, as well as decreasing the service life of the bearings.
An unresolved need therefore exists for an improved furling sail system.